How to create queue group consumer with new jetstream api.

[gudron]

Hello...i am looking for new jetstream API and i cant find replacement flow for old API.

How to create queue-group consumer?
How to create channel based consumer?
How to create push-type consumers?
How to create consumer for one-to-many communication model?

How long NATS community will support for old API?

old API just bttr...sorry

[Jarema]

The new JetStream API leverages fully the Pull Consumer.

1. You do not need to create queue-groups with Pull Consumer. It will load balance the load across all subscriptions to that Consumer.

2. The new API provides Messages, that delivers messages when calling Next, which can deliver the same uses cases that channel based did.

3. No push consumer support as of now, as with improvement of Pull Consumers over the time, the use cases between Push and Pull overlapped.

4. One to many:
   You mean one publisher and many clients receiving all messages?
   First of all, I would consider if that requires JetStream at all. If yes, and you need persistence, the solution is to create many consumers on the stream. Each will get its copy of the messages.

5. There are no concrete plans to move old API out of support. Howewer, some new featues, like multiple consumer fitlers, are not very ergonomic to use with old API. Also the old API does not allow for immediate consumption of messages for Pull Consumers (user need to aggregate all messages received in Fetch, while new API delivers messages as they arrive), nor it has a way to continously get the messages (user have to loop Fetch). Some new features might land only in new API.

[jnmoyne]

Functionally the new JS API has almost all of the functionalities of the old API (the only missing being 'push consumer without a queue group', which in my experience is never (or almost never) needed) and some new ones (e.g. support for acks=none or acks=all). And the performance is in most cases equivalent or better with the new API than with the old one.

[gudron]

(the only missing being 'push consumer without a queue group', which in my experience is never (or almost never) needed)

push consumer without a queue group is the easiest way for Choreography SAGA pattern ... sagas on pull-type consumers...srsly?

[Jarema]

@gudron both Push and Pull consumers serve as the API for the same server construct - Consumers.

The main difference is how the handle backpressure, by triggering messages requests versus flow control.
Pull Consumer is much more efficient at that.
They also have some difference how you load traffic (many clients vs many clients with queue-groups), but the result is functionally, again, the same.

From user perspective, there is no use-case difference between Consume/Messages on Pull Consumer, or Subscribe on Push.
Both provide you messages at quick rate, with the same latency, but Pull at the same time is much better at handling backpressure.

Please elaborate how those internal differences affect SAGA pattern.